Thickness effect of engineered cementitious composites subjected to quasi-static and dynamic tension

Engineered cementitious composites (ECC) showed promising potentials in structural protection against quasistatic and dynamic tension due to their superior tensile ductility. To facilitate its application as reinforcement layer of existing reinforced concrete structures, the thickness effect of ECC in terms of ultimate tensile strength and tensile strain capacity was experimentally investigated. The influence of the strain rate effect, the specimen thickness, and their coupling were examined and discussed in detail. It was found that ECC exhibited significant strain rate effect when subjected to uni-axial tension of strain rate ranging from 10-5 /s to 100 /s. Compared to those obtained from standard specimens under quasi-static loading, the ultimate tensile strength increased by 338%, and the tensile strain capacity decreased by 62%, respectively, under strain rate 100 /s. Particularly, the strain rate effect was observed more remarkable under relatively higher strain rates, i.e. from 10 /s to 100 /s. Moreover, subjected to a certain tensile loading rate, both the ultimate tensile strength and tensile strain capacity decreased with increasing specimen thickness. The degradation of strength was relatively slower under a higher strain rate, i.e. 50 /s and 100 /s, than under a lower strain rate. To facilitate the design of the ECC reinforcement layer, a formula was proposed capable of predicting the ECC ultimate tensile strength simultaneously considering both the strain rate effect and specimen thickness effect.